The invention relates to a fiber-optic device for illumination of a light permeable information-bearing medium, such as a traffic, information or advertising sign, which comprises one or more preferably plastic panels, arranged over each other, operating as a display device, in which the light issuing from the fiber-optic device propagates parallel to a display plane thereof, which have means for two-dimensional or planar light distribution and in front of or on which transparent information entities are arranged.
So that the traffic, information or advertising sign is designed so that it is sufficiently visible in poor lighting conditions (nights, tunnels, eta), self-illuminating systems are increasingly utilized in addition to signs and billboards that are lighted from the outside with headlights. A closed system with a transparent (glass) front panel with interior illumination, preferably by fluorescent lights, is standard according to the state of the art.
The essential disadvantages of this prior art embodiment include the following: problems with water-tightness, susceptibility to vandalism, expensive maintenance and a comparatively uneven or nonuniform optical appearance of the illuminated sign.
On the other hand, fiber-optically illuminated information-bearing media are known which have no weaknesses in regard to the above-described mechanical properties and which also have a clearly improved appearance.
In the fiber-optically illuminated information-bearing medium described in German Patent Document DE 295 08 596 U1 the information bearing-medium to be illuminated comprises one or more plastic panels arranged on each other which are illuminated by fiber-optic means parallel to the display plane. Microstructures in the panels or mechanical modifications in the panels arranged over each other in a multi-panel system, which are typically made of acrylic glass, provide uniform light distribution over the entire panel surface. In microstructured panels the information entities to be illuminated are placed on or in special foils or sheets (e.g. "Diamond Grade" of 3M) that are glued outside on the panels to illustrate the desired information entities.
The fiber-optic component used is designed especially for the dimensions of the display to be illuminated. In most cases a discharge lamp is used as the light source.
In the known embodiments the light guide bundle is directly coupled with its light output ends at the plastic panels. Because of that the penetration depth of the light diffusely leaving the fiber-optic device in the object to be illuminated is limited. Also when the power of the lamp illuminating the fiber-optic components is increased, the light density gradient in the object itself is comparatively large. Further because of that the length of the individual arms of the fiber-optic device is limited, whereby the maintenance of the sign, which must be performed in comparatively inaccessible locations (e.g. over a road), is made more difficult.
Since a unique fiber-optic illumination arrangement is designed and built for each display in the current state of the art, currently such fiber-optic devices are very expensive and have high production costs.